Four (4) large air handling units (AHUs) in one of the buildings have heat recovery; however, only two (2) were operating efficiently.

The heat recovery system supplies a 50% glycol solution to the four (4) heat recovery coils in AHU-1A, AHU-1B, AHU-1C, and AHU-1D. The system utilizes a single 100 HP constant flow pump which operates when the outside air temperature decreases below 54°F and is disabled when the outside air temperature rises above 55°F.  The exhaust side of the heat recovery system is comprised of nine (9) coils located in the fume exhaust system.

The heat recovery was operating as follows:

AHU-1A: There was less heat recovery occurring. The heat recovery return water temperature was higher than AHU-1B and AHU-1C.

AHU-1B: The heat recovery system was operating efficiently.

AHU-1C: The heat recovery system was operating efficiently.

AHU-1D: There was less heat recovery occurring. The heat recovery return water temperature was higher than AHU-1A, AHU-1B, and AHU-1C.

This issue was not detected onsite because there was partial heat recovery occurring from the exhaust side.  In addition, the AHUs were able to maintain discharge temperature utilizing the preheat coils so there were no low temperature alarms.

However, the issue was identified with Analytika.  The root cause of the fault was that the heat recovery valves were not opening completely and the water was bypassing the coils.

Heat Recovery Analytics

Solution

Cimetrics worked with GBP staff and the controls vendor to fix the valves that were not opening, to maximize heat recovery for all four (4) AHUs.

Annual energy savings achieved: $34,852

Annual carbon emissions reduction: 605 metric tons

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